This invention relates to a disposable undergarment adapted to absorb body exudates and to retain them.
Japanese Patent Application Publication No. 1997-140742A discloses a disposable diaper comprising a liquid-pervious topsheet, a liquid-impervious base sheet and a liquid-absorbent core disposed between these sheets wherein a front or a rear waist region of the diaper is provided with an indicator enabling a caretaker to detect whether urination has occurred or not from the exterior.
The indicator comprises a hydrophilic substrate sheet, a first coating layer printed on one side of the surface of the substrate sheet so that its initial color becomes distinct as it is wetted with urine, and a second coating layer printed on the first coating layer so that it normally conceals the first coating layer but becomes transparent as it is wetted with urine. The substrate sheet is formed by breathable but a liquid-impervious film obtained by stretching a plastic film containing particles of inorganic fillers such as titanium dioxide, barium sulfate or calcium carbonate. The substrate sheet has white or milky white color and a luminous transmittance in a range between 30 and 70%.
With this diaper, the indicator is intermittently bonded to the surface of the base sheet facing the wearer""s skin. A pattern defined by the first coating layer becomes distinct and the second coating layer becomes transparent as the indicator is wetted with urine. The pattern is distinctly vidible from the side facing away from the wearer""s skin so that occurrence of urination can be visually recognized by the helper from the exterior.
The above-cited Publication discloses one example of the base sheet formed by a composite sheet consisting of the plastic film and a fibrous nonwoven fabric bonded to this plastic film so that the plastic film defines the surface facing the wearer""s skin and the nonwoven fabric defines the surface facing away from the wearer""s skin. With the diaper using such a composite sheet as the base sheet, a feeling of touch with the base sheet is more or less improved but a luminous transmittance of the base sheet is reduced by the fibrous nonwoven fabric in comparison to the base sheet formed by the plastic film alone. No description on the luminous transmittance of the composite sheet is found in the above-cited Publication. Depending on the luminous transmittance of the composite sheet, there is a possibility that the pattern might be concealed by the base sheet and it might be difficult for the helper to visually recognize the pattern from the side of the base sheet even when the pattern is wetted with urine and the pattern itself becomes distinct. Additionally, the base sheet having its luminous transmittance reduced by the presence of the nonwoven fabric makes it difficult for the helper to visually recognize color change of the core to pale yellow due to urination from the side of the base sheet facing away from the wearer""s skin. In this case also, it is apprehended that the helper could not detect from the exterior of the diaper whether urination has occurred or not.
It is an object of this invention to provide a disposable undergarment enabling a helper to detect whether urination has occurred or not from the exterior of the undergarment even when its base sheet comprises a plastic film and a fibrous nonwoven fabric.
According to this invention, there is provided a disposable undergarment comprising a liquid-impervious base sheet having a wearer""s skin side surface and an undergarment side surface and a liquid-absorbent structure lying on the wearer""s skin side surface.
The disposable undergarment further comprises that the base sheet comprises a breathable but liquid-impervious inner sheet to define the wearer""s skin side surface and a fibrous nonwoven outer sheet joined to the wearer""s skin side surface to define the undergarment side surface, and the base sheet having a total luminous transmittance in a range between 60 and 85%.
Embodiments of this invention includes: the liquid-absorbent structure comprises a liquid-absorbent core and a liquid-pervious topsheet covering the core; the inner sheet is formed by an oriented plastic film containing particles of inorganic fillers and has a total luminous transmittance in a range between 65 and 90%; and the outer sheet is made of a nonwoven fabric of thermoplastic synthetic resin and has a basis weight in a range between 10 g/m2 and 50 g/m2 and a surface friction coefficient in a range between 0.05 and 0.3 wherein the synthetic resin fiber has a fineness in a range between 0.01 DTEX and 10 DTEX.